1. Field of the Invention
This invention relates to loading dock equipment and in particular to dock levelers which are used to span the distance between a loading dock and the bed of a vehicle. Specifically, it deals with increasing the strength and resistance to fatigue failure of the lip assembly, and with reducing the number of components and thus decreasing manufacturing complexity.
2. Prior Art
A conventional dock leveler has a deck assembly which stores level with the dock floor or vertically, and a pivoting lip assembly which extends outward to rest on the vehicle which is being loaded. The deck assembly can be of various structural configurations with structural beam members used to provide strength and rigidity to the top plate. However the lip assembly must be of a much thinner section to minimize the height difference between the top of the deck assembly and the bed of the transport vehicle. Also, the lip must hinge downward approximately 90 degrees to store the dock leveler or to allow the lip to be removed from the vehicle for end loading the last pallets at the end of the vehicle. These constraints have traditionally caused the lip assembly and hinge to be the weakest parts of the dock leveler structure. Increasing the thickness of the hinge tubes and the lip plate will increase the strength but at a significant weight and cost penalty. Also, gusset plates welded between the hinge tubes and the lip plate have been used to increase the strength. U.S. Pat. No. 5,071,306 shows an improved hinge construction with a continuous weld between the gusset and the lip plate to improve resistance to fatigue failure of the lip.
One limitation of the hinge tube construction is that the distance from the hinge pin to the lip is determined by the diameter of the tube. If the distance can be increased, then the load on the hinge pin will be reduced while providing the same resistance to rotation of the lip. The construction shown in U.S. Pat. No. 4,068,338 uses a series of plates or xe2x80x9clugsxe2x80x9d attached to the deck and the lip plate. Thus the position of the hole in the hinge lug rather than the thickness of the hinge tube determines the location of the hinge pin. Although the strength of the hinge can be increased using the lug design, the lip is still prone to fatigue failure at the tip of the lug welded to the lip plate.
This invention is a new type of lip assembly and method of construction that significantly increases the strength and resistance to fatigue failure of the lip assembly of a dock leveler. In accordance with this invention a dock leveler has a frame, a deck hingedly mounted at one end to the frame and a lip hingedly mounted to the deck at another thereof. In the first preferred embodiment, the lip has a hinge that is formed from a flat plate that is bent to form a hinge pivot at the desired distance from the lip plate. The forward edge of the hinge forms a continuous gusset affixed to the lip plate. The rear edge of hinge has a plurality of segments that are affixed to the lip plate. The hinge is preferably formed from a single piece, but may be constructed of several segments joined together. Slotted openings are cut in the rear edge of the hinge. Hinge lugs are welded to the front of the deck and fit into the slotted openings of the lip hinge. A hinge pin is passed through the lip hinge and the lugs to secure the lip to the deck.
The lugs on the deck and the single piece lip hinge provide a number of structural and manufacturing advantages. The continuous gusset formed by the front edge of the hinge provides the greatest resistance to fatigue failure at the attachment to the lip. Compared to the conventional hinge tube construction where each alternating segment is attached to the lip and the segments in between coupled to the deck, the formed lip hinge provides twice as many hinge segments transferring load from the lip to the hinge pin. The hinge segments fitted between the lugs provide the hinge pin with twice as many shear joints as the prior art lug hinge, significantly reducing the stress at each joint. Both features significantly decrease the stress and improve the fatigue strength of the lip hinge. The single piece hinge also improves manufacture by eliminating the number of parts and manufacturing operations.
A second preferred embodiment has hinge lugs on both the lip and the deck and gussets welded to the lip plate and the lip lugs to form a continuous weld across the lip plate. Although this preferred embodiment does not provide the improvements in strength of the lip hinge, it does provide the improved resistance to fatigue failure at the junction of the hinge lugs to the lip plate.
This invention will be described in greater detail by reference to the drawings and the description of the preferred embodiments, which follows.